Correction of iron deficiencies in growing plants



United States Patent,

CORRECTION OF IRON DEFICIENCIES IN GROWING PLANTS Alexander A. Nikitin, College Park, Ga., assignor to Tennessee Corporation, New York, N. Y., a corporation of New York No Drawing. Application February 20, 1956, Serial No. 566,394

6 Claims. (Cl. 71-1) This invention relates to the correction of chlorotic conditions in plants grown in soils lacking adequate amounts of iron in available forms. This application is a continuation-in-part of my prior applications Serial No. 336,640, filed February 12, 1953, now abandoned; Serial No. 353,914 filed May 8, 1953, now abandoned; and Serial No. 510,524 filed May 23, 1955 as a continuation-in-part of Serial No. 336,640.

It is well known that soils deficient in certain minerals known to be essential do not produce vigorous healthy plant growth. In particular, iron deficiency results in a diseased condition known as chlorosis because of loss of chlorophyll and consequent yellowing of foliage. Correction of such chlorotic conditions can be attempted by the application of iron compounds either to the soil or to the plant itself. Prior to the present invention, however, the results obtained by these methods were unsatisfactory. Itappears that iron deficiency is the most diflicult of all trace element deficiencies to correct. Tests at the Florida Experiment Station showed that soil treatment and sprayingwith ordinary iron salts and iron chelates were ineffective. These results also proved that when regular soluble salts, such as iron sulfate, were used for soil treatment, iron was not taken up from these soluble salts apparently due to hydrolysis and consequent formation of iron oxide. Also spray treatments using iron sulfate or iron oxide were not effective, causing green spots to form on the leaves. New growth on deficient plants, following these sprays, Was usually chlorotic. The ineificiency of sprays containing ordinary iron salts in correcting iron chlorosis has been interpreted as a result of rapid immobilization of these iron salts in the plant leaves.

The present invention involves the discovery that when ferrous oxalate is applied to the chlorotic plant or added to the soil'in which it is growing, chlorotic conditions are very rapidly eliminated. In comparative spray tests with chelated iron and some other iron compounds, on adjacent plots, ferrous oxalate was applied as a spray to numerous subtropical ornamental trees, shrubs and grasses,

which previously had shown extreme chlorosis. The restoration of these plants to a deep green color was outstanding and rapid in the case of ferrous oxalate treatment.

Ferrous oxalate can be used very efiectively to correct iron deficiencies of both acid and alkaline soils. At the above-mentioned Florida Experiment Station at Homestead, Florida, for example, the soil is very alkaline and has a pH of about 8. It can be applied to the soil in any suitable manner, being simply mixed with the soil preferably by admixture with other fertilizer materials. For treatment of foliage, it is safe to use and does not injure the plant. It can be applied as a dust or spray, and in either case it can be mixed with organic insecticidal and fungicidal materials with which it is compatible. The amount to be used'will vary depending on the extent of the soil deficiency, the ages and types of the plants to be treated, the rainfall, etc. For most purposes from 1.0 to 4l bs. per 100 gallons of spray water will give best re- Patented Nov. 27, 1956 sults. The concentration at which ferrous oxalate is used as a dust ranges from 4 to 12 lbs. of ferrous oxalate per lbs. of dust mixture. The optimum concentration in any case depends upon the severity of chlorosis in the plant.

The exact mode of action of ferrous oxalate cannot yet be stated with certainty. It is apparently somewhat similar to that of the chelating agent now on the market (ethylenediamine tetraacetic acid), but more effective. Ferrous oxalate apparently retains iron in a non-ionic state, even under severe conditions. Even after remaining in the soil for long periods, the iron is much more readily available to the plants than in the case of other iron compounds heretofore tested. Also ferrous oxalate acts as a buffer against any toxic effects of excessive quantities of manganese that are sometimes present in the soil. On foliage, ferrous oxalate causes no injurious effects, remains for a long time Without leaching away, and is most effective in correcting chlorotic conditions and promoting rapid recovery of the plants.

In summary, the advantages of using ferrous oxalate for the above purposes include:

1. It is chemically stable, even when exposed to atmospheric action over long periods of time, and especially when exposed to sunlight.

2. The inherent physical properties of ferrous oxalate, as received from the dryer, are such that it doesnot need additional grinding, being very finely divided. Ferrous oxalate thus may be spray-dried or flash-dried, making the manufacturing process extremely economical.

3. Ferrous oxalate is much more economical in comparison with chelated compounds, from the standpoint of low cost of the raw materials and plant equipment, and simplicity in its manufacture.

4. From the safety standpoint, ferrous oxalate is particularly valuable since it can be used for plant treatment at a wide range of concentrations, without causing any injury. Overdosing does not cause plant injury. From 1 to 4 pounds per 100 gallons of spray have been used safely; however, these amounts are not limiting.

5. Ferrous oxalate is compatible with insecticidal and fungicidal materials in general.

6. Soil application of ferrous oxalate shows promising results on vegetable crops.

As already noted, the above named advantages render ferrous oxalate superior to other iron salts and highly advantageous for use. The related compound ferric oxalate, for example, causes foliage injury, even when used for foliar treatment at very low concentrations as compared with ferrous oxalate. Furthermore ferric oxalate is not compatible with insecticidal and fungicidal materials, is unstable and decomposes on exposure to sunlight and is much more difiicult to manufacture and more expensive to use than the ferrous salt. Above all, however, in comparative tests on adjacent plots ferrous oxalate was eifective in restoring deep green color, for'example in green peppers, while ferric oxalate produced no detectable recovery to green color but instead caused injury to foliage. I

The reasons for these surprising diiferences in resultsare obscure and not fully understood at present. How-- ever, ferrous oxalate has been used successfully to restore healthy green color to chlorotic iron-deficient plants of wide variety including ornamental shrubs such as azalea, camellia, gardenia, hibiscus, and rose, vegetables such as green peppers, potatoes and tomatoes, grains such as corn, oats, and sorghum, grasses such as centipede, St. Augustine, carpet and Pangola, and fruits such as citrus, blueberries, peaches and strawberries.

Although as stated above and in my aforesaid patent application Serial No. 353,914, ferrous oxalate isv compatible with fungicidal and insecticidal materials in gen cases.

etal, -iLhaS been. found that notthe ..case .withrei gard to one of the most widely used inorganic fungicides, V 1. e., basic coppersulfate (e; g., CuSO43Cu(OI-I)2-H2O).

It/ PP'ears that ;the ferrous oxalate: reacts with: the basic copperlsulfate with a resultant undesirable'incr'ease in I thesolubility of both materials and injury to thefoliage of the. growing plant.

, The incompatibility of ferrous oxalate and basic copperv sulfate in thepabsence of a stabilizing agent is evident from .the facts that the solubility of ferrous oxalate in water at .ordinary temperatures is only about 6 p. p 111., andthat of basic copper sulfateis vonly about 3 p. p. m., whereas .whenlthey are mixed together in. approximately equalproportions, the solubility of 'the'ferrous oxalate increases 'to 130 p. p. m. and thatofthe basic copper sulfate", increases to 160 p. p. 'm. The known practice of using-alkaline: materials, such as-calcium and magnesium V hydroxides and sodium carbonate, to reduce the solubility possible the conjoint use of ferrous oxalate and basic copper sulfate on growing plants, by the combination of thesetwo materials with a stabilizing agent which reduces or'prev'ents the aforesaid reaction and thus practically eliminates the' aforesaid adverse eifects on the growing plants, but which does-notinterfere with the desired beneficial effects on the plant" j It has -now been found that the foregoing disadvantage canbe eliminated and that ferrous oxalate is rendered compatible with basic copper sulfate when these two materials are combined with a third material selected from the.foll-owing group, namely, basic zinc sulfate, basic zinc carbonate, zinc oxide, basic zinc chloride, basic zinc chloride sulfate, tribasic zinc phosphate, manganous oxide, manganic oxide and manganese dioxide. Of these materials, basic zinc sulfate appears to be the most effective stabilizing agent and is therefore preferred in most But manganous oxide can be used to advantage in cases of manganesedeficient soils.

The amount of stabilizing agent to be added to'th mixture of ferrous oxalate and basic copper sulfate may be relatively small. For example, from 6 to '10 parts by weight of basic zinc sulfate (e.

a mixture containing equalparts of ferrous oxalate and basic copper sulfate. In such a combination, the solubility'of the copper compound is only about 6 p. p.'m. and the solubility of the ferrous oxalate is only about 10 pp. in, as compared with 160 p. p. m. and 130 p. p.111. respectively ina the absence of the basic zinc sulfate as stated above. l 7

Basic zinc carbonate and the other zinc compounds.

. g-Q' ZnSO4-4Zn(OH)z-2H2O) can be used with 100 parts of .rlous oxalate:basicrcopperqsulfateumixture, butrordinatily at least 6 parts are desirable. On the other hand, increasing the amounts of the stabilizing agents above the values set forth above is permissible, and may be de sirable where this agent ,is tolcontribute a nutritional or other beneficial eifect in'addition to its stabilizing action. In any event, however, the amountofthis third ingredient will not exceed the combined amounts of the other two,

and as a rule it will fall within the ranges given above.

Thecombinationof ferrous oxalate and basic copper sulfate with a stabilizing agent such as .basiozinc sulfate, for'example, makes'it possible to apply thenutritional iron and the copper fungicide to the growing plant in a single spray or dust treatment. Not only are time and labor thus saved, but :also the possibility ,ofsimultaneous application of both materials permits immediate treatment of the plant for either nutritional deficiency or fungus disease whenever they appear-and avoids :delays thatwould otherwise necessarily intervene between successive applications of ferrous oxalate and basic'copper sulfate; Field tests have shown that the ferrous oxalate in such compositions retains its efiectiveness in supplying nutritional iron to the plant as disclosed in my aforesaid application, and that the basic copper sulfate retains .its normal fungicidal properties but is harmless to the plant.

A further advantage of the combination of ferrous oxalate with basic copper sulfate and'a stabilizing agent resides in the unusually good adherence of this composition tofoliagewhich is of greatimportance, especially in the .case of glossy citrus foliage which in most "case'sism sprayed onlytwiceayear; :Basic coppersulfateisinot' naturally adherent and an appropriate adhesiveisznecs; sary to prevent washing away of the spray residue under normal conditions of rainfall. But commerciallyavail-" able adhesive materials are very specific in their performance, and also. must be tested for their compatibility withibasic copper sulfate since many of them-reduce the availabilityof the copper and thus .the-desired'fungicid'ale'ffect. Ferrous oxalate, however, is naturally a powerful adhesive material, and in the presence of basic zincsulfate it acts as a superior adhesive'for basic copper-sulfate as shown by the following tabulated com-' mentioned can be used in about-the same concentrations as basic zinc sulfatey-butthemanganese compounds are somewhat lesseifective. 'For example, when manganous oxide is used in the proportion of 610 parts to 100 parts of a mixture containing equal parts of ferrous oxalate and basic copper sulfate the solubility of the basic copper sulfate is about 40 p. p. m. and that of ferrous oxalate is about 10 pp. m., as compared with the values setforth above in the case of basic zincsulfate. ,By increasing amounts of the stabilizing agents may be permissible.-

For example, basic sulfate is an; effective stabilizer in concentrations as low"as 4 parts-per loll parts offerparison with other conventional adhesives. In thesetests, two pounds of adhesive material'andfour pounds of-basic copper sulfate were usedper 100 gallons of water. About onegfour'th pound of basic zinc sulfate was also used in each test. I

, Cir-deposit in pig/cm} I a a 1 'Percent Adhesive material 7 I I I adhesive Just after 10 da s after spraying spraying 1. Ferrous oxalate 3i33 2.46 f7410 2. *Bentonite j 2. 1, 02 :36. 0 3. So ya flour" 2.90 0.65 p 22.5 4. Caseiruus 3.1.2 0. V 0

, Thus spray residues from compositionsernbodyingthe invention remain 'on the foliage of the plant even when subjected to..heavy.rains following application, as shown by the above results. This improvement in adherence *of the spray' residues containinglferrous ioxalate is ofhigher,

a n h n the pray mpqs t on als con a ns' as zinc sulfate which renderslitsafe for plants. 1 Also the ferrous oxalate retains its effectivcues as .ajnutritional material as shown by the rapid response o'fQchlorotic citrus plafnts, and grasses in field vtests,,,whereas, no :copper injury.,appears when basic zinc-sulfate is included." 1"hus immediate. application of the mixturejcan be .made whenever either. nutritional. deficiency or fungus infecting appe s. an ful d a a n be taken of he co om asipgle application for bothpurposes;

;Sev e'ral' processes are known for "themanufacture of ferrous-oxalate: which can be used in;preparing-thepi aterial for the-abov e purposesgbut the 'followiug proeedu're is preferred in which ferrous sulfate is reacted with oxalic acid. It has been found that this reaction is essentially complete at a temperature of 160 F.-170 F., but that temperatures higher than 170 F. during the reaction or subsequent drying may cause decomposition.

The following is an example of the preferred process:

75 pounds of ferrous sulfate (FeSOrJHzO) were dissolved in 50 gallons of water, and 30 pounds of technical oxalic acid (H2C2O4.2H2O) were dissolved in 20 gallons of hot water in a separate tank. The amounts of iron sulfate and oxalic acid used were not the same as would be used on a molecular ratio basis because both materials were of technical grade. The oxalic acid solution was added to the ferrous sulfate solution and heated, with agitation, to l60170 F. for about 1 hours at the end of which the reaction was complete and a bright canary yellow color had developed. The reaction was as follows:

The ferrous oxalate precipitate was allowed to settle, and was washed with water, by decantation, until most of the soluble sulfates were removed. The ferrous oxalate sludge was then filtered on a rotary filter, with washing until the filter cake, in water suspension, had a pH of 6.8-7.0. The filter cake Was dried at a temperature not above 170 F. This cake was finely divided and suitable for either spray drying or flash drying in actual production.

It will be understood that the invention is not restricted to the details set forth in the foregoing description, since various changes can be made without departing from its spirit. Reference should therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is: V

1. The method of supplying nutritional iron to plants growing in iron-deficient soil which comprises supplying iron to the plant in the form of ferrous oxalate in contact with the tissues of the growing plant.

2. A nutritional and fungicidal composition for application to the foliage of growing plants comprising a mixture of ferrous oxalate and basic copper sulfate containing a minor proportion of a stabilizing agent selected from the group consisting of basic zinc sulfate, basic zinc carbonate, zinc oxide, basic zinc chloride, basic zinc chloride sulfate, tribasic zinc phosphate, manganous oxide, manganic oxide, and manganese dioxide.

3. A composition as defined in claim 2, containing about 6 to 20 parts by weight of said stabilizing agent to parts of said mixture.

4. A composition as defined in claim 2, said mixture comprising substantially equal proportions of ferrous oxalate and basic copper sulfate and said composition containing about 6 to 20 parts by weight of said stabilizing agent to 100 parts of said mixture.

5. A nutritional and fungicidal composition for application to the foliage of growing plants comprising a mixture of ferrous oxalate and basic copper sulfate in substantially equal proportions and containing 6 to 10 parts by weight of basic zinc sulfate to 100 parts of said mixture.

6. A nutritional and fungicidal composition for application to the foliage of growing plants comprising a mixture of ferrous oxalate and basic copper sulfate in substantially equal proportions and containing about 20 parts of manganous oxide to 100 parts of said mixture. 

1. THE METHOD OF SUPPLYING NUTRITIONAL IRON TO PLANTS GROWING IN IRON-DEFICIENT SOIL WHICH COMPRISES SUPPLYING IRON TO THE PLANT IN THE FORM OF FERROUS OXALATE IN CONTACT WITH THE TISSUES OF THE GROWING PLANT. 